The invention relates to a process for coating a substrate surface with a permeation barrier of inorganic material, which is vaporized from a crucible in a vacuum chamber evacuated to at least 10.sup.-3 mbar and precipitated on the substrate surface. The invention also relates to a coating implement for carrying out and applying the process.
Thermal vapor deposition is the process used most often for producing optical coatings. It is because of these layers that it has been recognized that essential mechanical properties of layers are inferior to those of corresponding solids. It has also been acknowledged that deposition processes using particles of higher kinetic energy than for a standard thermal deposition lead to improved mechanical properties. Ion-assisted deposition (IAD=Ion Assisted Deposition) is one of these deposition processes.
German Patentschrift 3 543 316 describes a process for reactive vapor deposition of electrically insulating layers on substrates with simultaneous partial ionization of the vapor by means of a low voltage arc discharge and acceleration of the ions produced onto the surface to be coated. A electric field is maintained between a vapor source as the anode and the substrate surfaces at negative potential compared to the anode. An electric plasma is produced by means of electric gas discharge in front of the surface to be coated during coating. The electric gas discharge is adjusted so that the substrate surfaces are charged to a potential of -5 to -60 volts compared to the plasma potential. The ion incidence density is 0.5-3 mA/cm.sup.2. The gases required for reactive vapor deposition to be reacted with the vaporized substance are supplied to the position of highest vapor density in front of the anode.
A transparent packaging film with low permeability to gases and liquids is known from U.S. Pat. No. 3,442,686. The 0.02 to 2 .mu.m thick gas and liquid barrier consists of an inorganic material of glass-like nature vapor deposited onto a plastic film. A further plastic film is applied to this barrier layer. The mechanical protection of the contents, protection against contamination and moisture, prevention of losses of package contents and the advantageous appearance are mentioned as main functions of the packaging film.
Several conveyer coating plants for plastic films using an electron beam vaporizer are known, for example from Messrs. Leibold, BVT or Galileo. The layers produced by known vapor deposition processes are not sufficiently compact, the density of the material is, for example for silicon dioxide, only 80% of the density of a solid from the same material.
A non-compact layer has a low stability and insufficient adhesion to the substrate. In order to retain stoichiometric layers with a reactive vapor blast process, the process must be carried out using high reactive gas partial pressure, as a result of which even less dense layers are produced.
Furthermore, hitherto known processes of reionization can be used only for small vaporizer sources and low coating rates, since they either cannot be scaled or have ionization rates which are too low.